The detection of low level photonic emission from chemical reactions in the field of bio-chemistry has become of increasing importance as techniques have been developed which involve the mixing of one or more reagents with blood serum or other body fluids to determine whether or not and to what extent antibodies or antigens or the like are present in the body fluid, depending on whether or not and how much photonic emission occurs following the mixing of the reagents with the body fluids. These techniques have been developed for mass screening of diseases such as certain cancers and latterly AIDS.
In such techniques, liquid samples to be tested are placed in each of the wells in an opaque tray typically formed from plastics material. A typical tray will comprise 96 such wells each of 6 mm diameter on a 9 mm spacing. The 96 wells form a 12.times.8 array. Each well enables a single test to be carried out with a particular reagent-sample combination. Thus the 96 wells together enable up to 96 tests to be carried out simultaneously with many possible combinations of different tests for one individual or the same test for different individuals.
The main problem associated with photonic emission diagnostic techniques is the very low rate of photon emission associated with most such reactions. The signal-to-noise ratio of most conventional electronic photo detectors is far too low to enable such low photonic emission to be detected and attempts have been made to improve the sensitivity of conventional photon detectors as by cryogenic cooling techniques to reduce the electrical activity of the detector, (and hence the noise), to an acceptable level, and thereby enable the detector to respond to very low photon emission rates.
However such devices still do not possess the level of sensitivity which is desirable since the coupling efficiency between the light output from the individual wells and the photon detector has tended to be very poor. Additionally the charge coupled devices normally used as such detectors tend to have a very low efficiency (typically of the order of 30%) at the wave length (typically 420 nanometers) associated with luminescent assay measurement.
The use of wavelength conversion layers to achieve higher efficiency has significant associated problems.
Other proposals have utilised imaging photon detectors the output of which comprises digital signals corresponding to the X,Y co-ordinates at which a photon event has been detected. However such devices operate on a random sampling basis and tend to saturate and become insensitive to low light level sources in the presence of high light level sources. Such devices therefore do not lend themselves to general use for testing sample trays where there can be considerable disparity between the photon emission from one well and from another.
Known proposals are also disadvantageous in other fields demanding low level light detection, such as gel electrophoresis.
It is therefore one object to the present invention to provide apparatus including an improved photon emission detector capable of a wide dynamic range and yet capable of responding to and producing an output signal in the presence of very low rates of photon emission.
It is further object of the invention to provide a luminescent assay measuring system capable of responding to very low photon emission rates for use in the detection of virus infections and cancerous cells, particularly in tissue sections as found in histology.
Moreover, in the microscopic examination of a sample on a microscope sample-holder, even at low magnification the operator sees only a small part of the sample at any one time, and is required to scan the entire sample to find any one or more sites of particular interest, which can then be examined in more detail at high magnification. Operator scanning of the entire sample in this way is time consuming and expensive, and therefore a further object of the present invention is to provide an image quantifier which assists in the solution of this problem.
However, the imaging apparatus of this invention is of general applicability in the fields of fluorescence microscopy, luminescence microscopy, interferometry, spectroscopy, X-ray digital imaging, and gel electrophoresis, for example, as well as in related fields of endeavour where high sensitivity optical imaging is required.